1. Field of the Invention
The present invention relates to variable displacement vane pumps and, more particularly, to an improved dual lobe, split ring, variable displacement roller vane pump. It finds a particular application as a pump for delivering fuel to an aircraft jet engine or gas turbine and will be described with particular reference thereto. However, it will be appreciated that the present invention is also amenable to other applications that can advantageously use the features of the variable output flow of the pump.
2. Discussion of the Art
Turbine engines on aircraft require variable amounts of fuel during operation. For example, the fuel flow needs of a turbine engine during takeoff are significantly different than during high altitude cruising and not proportional to the speed of the engine. To accommodate these changing needs, in the present state of the art, fuel is pumped to the engine using a fixed positive displacement pump in conjunction with a variable delivery fuel system.
Variable delivery has been achieved in a number of different manners including changing the geometry of the positive displacement pump and/or bypassing a portion of the excess pumped fuel back to the pump inlet. Generally, bypass systems have been favored in the industry. In such a system, the delivery of variable fuel flow to the engine is achieved by selectively bypassing excess flow to an interstage or inlet of the positive displacement pump.
Conventional positive displacement pumps include gear pumps, vane pumps, or piston pumps. When the variable delivery system is a bypass system, the pumps are typically fixed displacement pumps that deliver a preset amount of fuel at a given speed. Such systems employing a fixed displacement pump and a bypass are heavy, inefficient and sometimes temperamental.
Variable displacement pumps, in contrast, have not been favored for the delivery of fuel to aircraft engines (pumps operating in the order of 8,000 rpm and 1500 psid). Although more efficient as a component, fixed displacement pumps have, heretofore, caused undesirable heating of the fuel in a fuel delivery system. Fuel system heating needs to be minimized in many advanced engine systems such as those used in aircraft applications.
Variable, positive displacement pumps operate by first capturing a controlled variable volume of fluid from the pump inlet, then pushing the captured fluid into a discharge line. Typically, variable displacement vane pumps are somewhat intolerant to contamination. Other shortcomings include vane tipping and excessive vane tip loading at inlet and discharge port openings, significant pressure pulsations and cavitation caused by fluid trapping in the seal arcs, high radial bearing loads, use of brittle vane, cam, and port plate material, high carryover volume at low flow, and use of complex mechanisms to synchronize movable multiple cam rings.
Accordingly, there is a need for a balanced, variable displacement pump that is more robust and contamination tolerant and does not cause undesirable amounts of fluid system heating. The present invention provides a new and improved variable displacement pump for overcoming the above-referenced drawbacks and other shortcomings.
The present invention relates to a variable displacement pump. More particularly, the present invention relates to a dual lobe, split ring, variable displacement roller vane pump for supplying, for example, an aircraft engine varying amounts of fuel.
In accordance with the present invention, an improved variable displacement roller vane pump is provided. The pump comprises a housing having an inlet and an outlet, a rotor having a plurality of slots rotatably mounted within the housing and a plurality of roller vanes operatively mounted within the slots. A pair of port plates are mounted on opposite axial sides of the rotor and two cam segments movably mounted around the rotor for selective radial movement relative to the rotor. Each cam segment has a curvilinear surface for cooperating with the rotor, the port plates, and the roller vanes to define a plurality of pumping chambers. The cam segments are independently movable to create varying volumetric pumping chambers along the curvilinear surface of the cam segments. The pump additionally comprises unique fluid communication passages for providing fluid into the pumping chambers from the pump inlet and for discharging the fluid from the pumping chambers to the pump outlet.
In accordance with one aspect of the present invention, a tongue and groove connection is provided between the cam segments for seamless transition of the roller vanes during rotation from one cam segment to the other.
In accordance with another aspect of the present invention, the port plates preferably include radially aligned inlet and cutlet channels for balanced fluid communication with the pumping chambers. The port plates also include radially aligned pressure inlet and outlet channels for balanced fluid communication with the slots beneath the roller vanes.
In accordance with another aspect of the present invention, the roller vanes are load supported in the slots by a shoe. Additionally, the shoe configuration prevents the roller and shoe from being improperly assembled in the rotor slot.
One advantage of the present invention is the provision of a variable displacement roller vane pump that reduces excess fluid flow to a system and the resulting energy loss and heating of the fluid being pumped.
Another advantage of the present invention is the provision of a rotor of a variable displacement vane pump that is normally xe2x80x9cpressure balancedxe2x80x9d to minimize the loads transmitted to the pump bearings.
Yet another advantage of the present invention is the provision of a variable displacement roller vane pump that may be used for a wide variety of applications.
Still another advantage of the present invention is the provision of a variable displacement vane pump that utilizes rollers as the vanes.
A still further advantage of the present invention is the provision of a variable displacement vane pump that is low in weight and total volume.
A still further advantage of the present invention is the provision of a variable displacement vane pump in which each cam segment can be independently controlled.
A still further advantage of the present invention is that the pump can be used with two independent discharges with a single inlet or two independent inlets with two independent discharges or any combination of the above.
Further advantages and benefits of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the preferred embodiment.